In a display panel comprising a display device and a driving device, electrical connections between the display device and the driving device are usually designed to maximize the number of connectors within an available real-estate between the two devices. In a liquid crystal display (LCD) panel, for example, a gate driver and a data driver are electrically connected to an LCD device in order to operate the LCD device (see FIG. 1).
A thin-film transistor liquid-crystal display (TFT-LCD) is a type of flat-panel liquid-crystal display (LCD) device composed of an array of pixels. Each pixel is controlled by a gate line and a data line. As shown in FIG. 1, the TFT-LCD device 200 is composed of an array of pixels 210 and is controlled by a data line driver IC 230 and a gate line driver IC 220. In FIG. 1, G1, G2, . . . , Gm are gate lines and D1, D2, . . . , Dn are data lines. Preferably, both the driver ICs and the TFT-LCD device are disposed on the same glass substrate. After fabricating the TFT-LCD device on the glass substrate, driver ICs are mounted on the substrate via a so-called chip-on-glass (COG) process. Each of the driver ICs and the LCD device has a plurality of connectors so as to provide the electrical connections between each of the driver ICs and the LCD device.
FIG. 2 only shows the electrical connections between the LCD device 200 and a driver IC 220, as established by the COG process, for example. As shown in FIG. 2, the connectors on the display device 200 include a plurality of conductive strip segments 332 connected to a plurality of bump pads 330. Likewise, the connectors on the driver IC 220 include a plurality of conductive strip segments 342 connected to a plurality of bump pads 340. When these connectors are connected together to provide electrical connections between the display device and the driver IC, each of the bump pads on the driver IC is superimposed on a corresponding bump pad on the display device. As shown, the bump pad is wider than the strip segment.
Referring to FIG. 3, as commonly seen in prior art, bump pads are arranged in a shifted pattern 350 so as to increase the number of bump pads in a unit length while maintaining a suitable distance between the two connectors. A typical completed display panel is shown in FIG. 3. As shown, the display panel 10 has a gate driver IC 220 and a data driver IC 230 electrically connected to the LCD device 200. The panel also has a strip of wires-on-glass 270 and a strip of wires-on-glass 272 separately connecting the gate driver IC 220 and the data driver IC 230 to a bonding tape 260 so as to provide electrical connection to a PCB 250 or the like. The shifted pattern 350 of the electrical connections is shown in detail in FIG. 4.
As shown in FIG. 4, the width of the bump pad is W1 and the length of the bump pad is W5. A gap W4 is kept between two adjacent bump pads. The thickness of the strip segment is W3. Given a pitch P between two connectors, the shortest distance between two connectors is W2, which can be determined as follows:P=W2+(W1+W3)/2.Due to the mechanical tolerance in the bump pad superimposing process, the acceptable smallest gap between two connectors is about 7 μm. If W1=23 μm, W2=7 μm and W3=5 μm, we have a pitch P=21 μm.
The demand for higher resolutions in display devices heightens the requirement for having more signal channels on a given area of the substrate. This means that the pitch should be reduced if possible. However, the width of the bump pad, W1, should not be further reduced, because the total area of the bump pad, W1×W5, should preferably be at least 2000 μm2 to provide a good electrical connection between a bump pad of the IC and a corresponding bump pad of the display device.
Thus, it is advantageous and desirable to improve the bump pad layout pattern so that the pitch can be reduced without changing the width of the bump pads or the width of the strip segments while maintaining the minimum distance W2 between two adjacent connectors.